Lubricant compositions



United rates @atent 3,063,943 LUBRHIANT CUMPOSETIQNS Morton Antler, Detroit, Micln, assignor to Ethyl Corporation, New York, N .Y., a corporation of Delaware No Drawing. Filed Sept. 8, 1958, Ser. No. 759,416 4 Claims. (iii. 252-4l6.4)

This invention relates to novel compositions comprising certain trimeric tin sulfide compounds admixed with a natural or synthetic base oil or grease.

In the compounding of functional fluids, various additives are used to impart certain desirable characteristics to the fluids. Thus, there are additives which impart antioxidant properties and additives which impart antiwear characteristics to fluids. In general, an additive is specific so that it performs but one function. It is the exceptional case Where an additive performs a variety of functions, such as anti-wear and antioxidant. A multifunctional additive is desirable since its use requires the blending of only one additive in the fluid and eliminates any possibility of a deleterious effect of one additive upon another in the same system.

Fluids used in lubricating systems operating at extreme pressures and temperatures are subjected to very severe conditions. In the presence of oxygen, they tend to oxidize, forming decomposition products which inhibit their lubricating efiect. Further, the fluids are subjected to high shear forces which tend to force the lubricant film from between the rubbing members so that effective lubrication is not obtained. Lubricants or fluids presently used in extreme pressure applications contain additives which corrode the rubbing surfaces so as to form films on the surfaces. These films act as a lubricant. Such additives are termed Extreme Pressure (E.P.) additives.

The BF. additives presently used have a number of drawbacks; for example:

(1) They, in general, have no antioxidant efiect upon the lubricant.

(2) The mechanism by which they function involves sacrificial corrosion of the rubbing surfaces.

(3) Their corrosion mechanism is ineffective in lubricating non-reactive rubbing surfaces.

A typical example of a commonly used E.'P. additive is carbon tetrachloride. This additive, when used in lubrieating a ferrous surface, breaks down in the lubrication system to form degradation products which react with the surface iron oxide coating to form a film of ferrous chloride. The ferrous chloride film then acts as a lubricant between the rubbing surfaces. Such an additive has little or no lubricating effect in a rubbing system in which the rubbing members are relatively non-reactive and resist corrosition. Typical examples or" such relatively non-reactive rubbing systems are titanium-ontitanium, stainless steel-on-stainless steel, and gold-onvgold. Other typical non-reactive materials are plastics,

such as nylon, polymethyl methacrylate, polyvinyl chloride, and polyethylene, and hard refractory ceramic materials such as tungsten carbide, aluminum oxide, silicon carbide and glass.

Rubbing systems may have relatively non-reactive surfaces for several reasons. First, the rubbing members may be composed of an inert material, such as gold which is essentially inert to any chemical reaction. Se" end, the rubbing members may have a tenacious oxide film which is non-reactive. Such a case is presented by 1 titanium which forms a tenacious surface oxide coating which is extremely non-reactive.

It is an object of this invention to provide new compositions of matter having superior antioxidant qualities and anti-wear qualities over a wide range of operating conditions. A more particular object is to provide such compositions of matter by adding to natural and synthetic base lubricant materials a single additive which-is multifunctional in its operation. A further object is to provide natural and synthetic base lubricant compositions which are effective in lubricating relatively non-reactive rubbing surfaces operating under extreme pressure conditions.

It has been found that the lubricity and oxidation stability of natural and synthetic baselubricants are greatly enhanced by adding thereto certain trimeric tin sulfide compounds. These compounds are employedin a concentration sufficient to increase the lubricity of the lubricant base material. In effecting lubrication, these additives are believed to function through two mechanisms. First, they may act as film formers. In film formation, the additive is degraded by the heat and pressure generated by the rubbing surfaces. This results in the formation of a film on the rubbing surfaces. The film is formed entirely from decomposition products of the additive. Thus, the film formation mechanism operates substantially independently of the chemistry of the rubbing surfaces and is effective in lubricating non-reactive surfaces which resist corrosion by a conventional E.'P. additive. Second, the additive may function through a corrosion mechanism'in the manner of a conventional E.P. additive. When lubricating reactive surfaces, both'mechanisms are involved.

In formulating my lubricant compositions, the trimeric tin sulfide compound may be present in a concentration range of from about 0.03 percent by weight to about 10 percent by Weight in the lubricant base material. The additive is found to be extremely effective at relatively low concentrations. Thus, a preferred concentration range is from about 0.03 percent by weight to about two percent by weight.

The trimeric tin sulfide compounds I employ have the following structural formula:

in which the radicals R R can be methyl, ethyl or hydrogen. If the R groups are all hydrogen atoms, the compound is l,3,5,2,4,6-trithiatristanninane. If the R groups are alkyl radicals, the resulting compounds are named as derivatives of 1,3,5,2,4,o-trithiatristanninane. In so naming the compound, the members of the ring are numbered one through six beginning on any of the sulfur atoms.

Illustrative examples .of these compounds are 1,-3,5,'.Z,4, G-trithiatristannine, 2,2,4,4,6,6-hexamethyl-1,3,5,2,4,6-trithiatn'stanninane, 2,2,4,4,6,6-hexaethyl-13,5,2,4,6-trithiatristanninane, 2,2-diethyl-4,4,6,6-tetramethyl 1,'3,5,2,4,6- trithiatristanninane, 2,6-diethyl-2,6-dimethyl 1,3,5,2,4,6- trithiatristanninane, 2,4, 6-triethyl 2,4,6-trimetl1yl-1,3,5,2, 4,6-trithiatristanninane, 2,2,4,4 tetraethyl 6,6-dimethyl- 1,3,5 ,2,4,6-trithiatristanninane, and 2-ethyl-6-methyl-1,3,5, 2,4,fi-trithiatristanninane.

These compounds can be prepared by reacting an alkyl tin halide compound such as dimethyl tin diiodide and diethyltin dibromide with sodium sulfide or hydrogen sulfide in absolute alcohol.

The tin compounds described above are superior antioxidants and anti-wear additives in a Wide variety of natural and synthetic base lubricant materials. For example, they improve the antioxidant and anti-wear qualities of mineral oils and greases; silicon-containing oils and greases including the siloxanes, silanes, and silicate esters; fluorocarbon oils and greases; diester oils and greases, aromatic ether oils and greases; phosphate ester Oils and greases; polyalkylene glycol oils and greases; synthetic hydrocarbon oils and greases formed from polybutene oils and other low molecular weight polyolefin 011s and tetrahydrofuran polymer oils and greases.

The mineral oils and greases include hydrocarbon oils and greases obtained through conventional refining processes of the petroleum crude stocks. Such conventional refining processes include distillation, solvent extraction, clay filtration, dewaxing, acid treatment and propane deasphalting. The constituents of mineral oils and greases may be summarized as (1) straight chain paraflins, (2) branched chain paraffins, (3) naphthenes, (4) aromatics and (5) mixed aromatic-naphthene-paratfin.

' The silicon-containing oils and greases include the polysiloxane oils and greases of the type, polyalkyl, polyaryl, polyalkoxy, and polyaryloxy such as the polymethyl slloxane, polymethylphenol siloxane and polymethoxyphenoxy siloxane. Further included are silicate ester oils, such as the tetraalkyl and tetraaryl silicates of the tetra-Z-ethylhexyl and tetra-p-tert-butylphenyl types and the silanes such as the mon'o-, di-, and tri-silanes. Also included are the chlorinated siloxanes such as the chlorophenyl siloxanes, and chloroalkyl siloxanes. Examples of typical silanes are diethyl dihexylsilane, dibutyl diheptylsilane, diphenyl diethylsilane and bis(n-dodecyl) dichlorosilane and his (n-dodecyl dioctyl) silane.

The fluorocarbons are compounds which contain carbon and fluorine. This class of compounds is analogous structurally to the hydrocarbons. Thus, the compounds are generally linear polymers built up of a recurring unit which is ll FF As used in the specification the term fluorocarbons is meant to include compounds which can also contain chlorine and hydrogen. Such compounds are linear polymers built up from a recurring unit such as iii; i It in which at least one X is fluorine and the other Xs are chlorine, fluorine or hydrogen. Thus, the fluorocarbon can be polytetrafluoroethylene, polymonochlorodifluoroethylene, polymonochloromonofluoroethylene and the like.

The fluorocarbons are chemically very stable. They possess high thermal stability and are quite resistantto oxidation. Their boiling points are similar to but are usually lower than the boiling points of the hydrocarbonsof equivalent structure.

The polyester oils and greases are esters formed by the reaction between polybasic acids and alcohols or monobasic acids and glycols. The diesters of branched chain aliphatic alcohols and straight chain dibasic acids have been found to be the most desirable polyesters for lubriof long chain linear polymers which are generally formed from the reaction of an aliphatic alcohol and an epoxide such as ethylene or propylene oxide. The products of such a reaction are complex and thus polyalkylene glycol lubricants may contain the ethers and esters of polyethylene and polypropylene glycol. (Also included within this terminology are the reaction products formed from higher polyalkylene oxides, polyglycidyl ethers and polythioglycols) These substances are manufactured and marketed in considerable quantities under the trade name Ucon. They are useful lubricants because of their fiat viscosity temperature curves, their low viscosity in the subzero temperature range as well as their low freezing points. They generally have viscosities at F. ranging from to 1200 Saybolt Universal seconds, flash points ranging from 300 to 500 F. and specific gravities ranging from about 0.97 to about 1.01.

Tetrahydrofuran polymer oils and greases are formed by the copolymerization of tetrahydrofuran and an alkylene oxide such as ethylene oxide. In the polymerization reaction the furan rings are ruptured forming straight chain tetrahydrofuran polymers to which the ethylene oxide groups are probably attached as side chains.

Polybutene lubricants are formed from the polymerization of isobutene. Isobutene, usually containing also some normal butene, is polymerized at low temperatures in the presence of a catalyst such as aluminum chloride to yield polymer oils of a wide range of molecular weights and viscosities. The polybutene oils have viscosities ranging from about 40 to over 3000 Saybolt Universal seconds at 210 F. corresponding to molecular weights from about 300 to 1500. Their flash points vary from about 200 to 500 F. and their pour points range from about -65 F. to about 35 F. The polybutenes have the same specification tests as petroleum oils, although they tend to have lower pour points, flash points and carbon residue than petroleum lubricants having an equivalent viscosity.

A variety of polymer oils, similar to the polybutenes, but utilizing other oletins of relatively low molecular weight are suitable as lubricant materials. These include polymers produced from propylenes, pentenes, hexenes, octenes, etc. or mixtures of the same. These various polymer oils are prepared in a manner very similar to the polybutenes and have physical properties of a similar order.

The phosphate esters are a class of lubricant materials whose chief beneficial characteristic is their lack of flammability. These materials, as characterized by the aryl esters of phosphoric acid, have good lubricity or oil-like properties, high film strength, resistance to heat and oxidation over a wide range of temperatures and are noncorrosive. Typical examples of such phosphate esters are .tricresyl phosphate, triphenyl phosphate, tr-ixylyl phosphate and the like.

The aromatic ethers are a class of compounds which are characterized in that a portion of the molecule contains at least two aryl groups bridged by an ether oxygen atom. The aromatic portion of the molecule may be substituted by halogen or alkyl groups. In general, these compounds have a high order of thermal and oxidative stability at high temperatures. They are further very stable toward radiation and thus will find future application in lubricating nuclear powered engines. Typical examples of these ethers are bis(methylphenoxy) benzene, bis(phenoxy) benzene, bis(chlorophenoxy) benzene, and bis(nonylphenoxy) benzene.

The following examples illustrate lubricant compositions of my invention. Unless otherwise specified, the proportions given in these examples are on a weight basis.

EXAMPLE I One part of 2,2,4,4,6,6-hexamethyl1,3,5,2,4,6-trithiatristanninane Was blended with 99 parts of a paraflinic, mineral'white oil having a sulfur content of 0.07 percent, a kinematic viscosity (ASTMD 445) of 17.15 centistokes at 100 F. and 3.64 centistokes at 210 F. The viscosity index of the base oil (ASTMD 567) is 107.5.

EXAM PLE II EXAMPLE III Ten parts of 2,2,4,4,6,6-hexaethyl-1,3,5,2,4,6-trithiatristanninane are blended with 90 parts of a grease comprising 12 percent of lithium stearate, 2.5 percent of polybutene (12,000 molecular weight), 0.2 percent of 4-tertbutyl-2-phenyl phenol and 85.3 percent of di(2-ethyl hexyl) adipate.

EXAMPLE IV Five parts of 1,3,5,2,4,6-trithiatristanninane are blended with 95 parts of bis(n-dodecyl) di-n-propyl silane. Bis- (n-dodecyl) di-n-propyl silane has a boiling point of 208 C. at 0.50 mm. of mercury, a melting point of C. and a density, d of 0.8181. Its viscosity is 14.76 centistokes at 100 F., 3.68 centistokes at 210 F. and 1.10 centistokes at 400 F.

EXAMPLE V Two parts of 2,4,6-triethyl-2,4,6-trimethyl-1,3,5,2,4,6- trithiatristanninane are blended with 98 parts of an aromatic ether which is bis(methylphenoxy) benzene. The bis(methylphenoxy) benzene is a mixture of isomers in which the methyl groups are ortha, meta, or para to the ether oxygen linkage. The mixture is liquid in the temperature range from 5 to 741 F. at 760 mm. pressure. Its viscosity is 550 centistokes at 32 F and it is thermally stable to 716 F.

EXAMPLE VI Four parts of 2,2diethyl-6,6-dimethyl-1,3,5,2,4,6- trithiatristanninane are blended with an LB-l65 polyalkylene glycol oil. The oil has a viscosity of 165 Saybolt Universal seconds (SUS) at 100 F. and 48.6 SUS at 210 F. Its viscosity index is 148, its ASTM pour point is -50 F., its flash point is 410 F. and its fire point is 460 F.

EXAMPLE VII Three one-hundredths parts of 2,2,4,4,6,'6-hexamethyl- 1,3,5,2,4,6-trithiatristanninane are blended with 99.97 parts of a commercial polybutene oil. The oil has a molecular weight of approximately 330, a viscosity of 114 SUS at 100 F., and a viscosity of 40.6 SUS at 210 F. Its viscosity index is 101, its flash point is 230 F., and its pour point is 65 F.

EXAMPLE VIII Six parts of 2-ethyl-6-methyl-1,3,5,2,4,6-trithiatristanninane are blended with 94 parts of a tetrahydrofuranethylene oxide copolymer oil. The oil has a tetrahydrofuranethylene oxide ratio of two to one, a Saybolt viscosity at 210 F, of 83 SUS and a Saybolt viscosity at 100 F. of 462 SUS.

EXAIVIPLE IX Eight parts of 2,2,4,4,6,6-hexarnethyl-1,3,5,2,4,6 trithiatristanninane are blended with 92 parts of a complex mineral oil base grease, comprising 13.8 parts of lithium stearate, 1.7 parts of calcium sterate, 33.8 parts of a California solvent refined parafiinic base oil (356 SUS at 100 F.), and 50.7 parts of a California solvent refined paraflinic base oil (98 SUS at 100 F.).

- seizure or welding of the balls.

6 EXAMPLE x Seven one-hundredths parts of 2,4,6- triethyl-2,4,6-trimethyl-1,3,5,2,4,6-trithiatristanninane are blended With 99.93 parts of tricresyl phosphate. Tricresyl phosphate has a viscosity of 25 C. of 285 SUS, its flash point is 250 0, its boiling range at 10 mm. of mercury is between 2 75 and 290 C. and its autoignition temperature is above 1000 C.

Many of my compositions were tested in a four-ball lubricant test machine to determine their lubricating effectiveness under various conditions. Two types of fourball machines were used. They are the Extreme Pressure Lubricant Tester (hereinafter referred to as the BF. tester) and the Four-Ball Wear Machine. The E.P. tester is described by Boerlage in Engineering, volume 136, July 14, 1933, pp. 46-47. The Four-Ball Wear Machine is described by Larsen and Perry in the Transactions of the A.S.M.E., January 1945, pp. 45-50.

The two types of machines are essentially the same in principle and differ only in their load ranges. The BF. Tester operates in the range of 10 to 800 kilograms and the Four-Ball Machine in the load range of 0.1 to 50 kilograms.

Both machines use four balls of equal size, arranged in a tetrahedral formation. The bottom three balls are held in a non-rotatable fixture which is essentially a universal chuck that holds the balls in abutting relation to each other. Since the bottom three balls are of equal size, their centers form the apices of an equilateral triangle. The top ball is afixed to a rotatable spindle whose axis is positioned perpendicularly to the plane of the non-rotat able fixture andin line with the center point of the triangle whose apices are the centers of the three bottom balls.

In operation, the four balls are immersed in the lubricant composition to be tested and the 'fixture holding the three bottom balls is moved upwardly so as to bring the three fixed balls into engagement with the upper ball. To increase the load, the fixture is moved upwardly and axially of the rotating spindle aflixed to the upper ball.

The effectiveness of the lubricant is determined by the amount of wear occurring on the lower balls at their points of contact with the upper ball. If the lubricant proves completely eflfective, the amount of wear is negligible. If the lubricant is not completely etfective, the upper ball may weld or seize to the lower balls. Such failure is due to the heat of friction generated at the contact points between the balls. A less severe type of failure is manifested by the occurrence of wear scars without In some cases the average diameter of the circular scar areas formed on the-lower balls is measured. This permits quantitative comparison of the effectiveness of a lubricant under two sets of conditions. As the severity is increased and higher loads are 'applied, the magnitude of wear and the likelihood of seizure or welding is increased.

In the tests reported herein the lubricity of compositions of the type of Examples I through X was compared to that of an additivefree base oil. The general conditions were the same in each test. The balls were one-half inch in diameter and made of SAE 52-100 steel. The speed of rotation of the upper ball was 572 r.p. m. and the temperatureof the lubricant was 50C.

To establish a base line for comparison, an additivefree parafiinic white mineral oil having a sulfur content of 0.07 percent, a kinematic viscosity (ASTM D 445) of 17.15 centistokes at F. and 3.64 centistokes at 210F. was tested at a number of loads. Each test was run for two hours after which the balls were disassembled and the average scar diameter of the lower three balls was determined. The results of these tests are shown in Table I. The scar diameters are average values obtained from a number of test runs.

Table I.Additive-Free Mineral Oil Load, kilograms: Scar diameter, millimeters Table lI.One-Tenth Percent Solution of Dimetlzyl Tin Sulfide Trimer in Mineral Oil Load, kilograms: Scar diameter, millimeters These results clearly demonstrate the effectiveness of a typical lubricant composition of my invention. As shown in Table II the use of my lubricant composition resulted in greatly reduced scar diameters over the entire load range from two and one-half to 40 kilograms. When it is considered that the volume of metal removed from the stationary balls varies in direct relationship to the fourth power of the scar diameter, these results are especially striking.

A further series of tests was conducted in the same manner as the above. In these tests, the lubricant composition comprised 0.068 percent of 2,2,4,4,6,6-hexamethyl-l,3,5,2,4,6-trithiatristanninane admixed with 99.932 percent of the same additive-free base oil. The results were:

Table III.-Sixty-Eight-Thousandths Percent of Dimethyl Tin Sulfide Trimer in Mineral Oil Load, kilograms: Scar diameter, millimeters These results show the efiectiveness of my additives at very low concentration. A concentration of 0.068' percent produced substantially the same efiect achieved with the use of 0.1 percent in Table II. Since cost is an important factor in formulating lubricant compositions, it is very desirable to use a low concentration of an expensive additive. My additives meet this criterion.

Further tests were run under the same conditions with a load of 40 kg. With a halogen-substituted polyphenylpolymethyl siloxane (Dow Corning F-60fluid), failure occurred at the end of eighteen minutes of operation. With the composition of Example 11 tested at 140C., successful lubrication was achieved over the two hour period at the 40 kg. loading. After the test the average scar diameter of the lower three balls was 1.04 mm.

Thus my composition gave successful lubrication for two hours whereas the non-additive lubricant failed in eighteen minutes. This represents an improvement in excess of six-fold.

' Similar results are obtained when using other of the lubricant compositions embraced within the scope of my invention. Thus the lubricant composition of Example 111 comprising ten parts of 2,2,4,4,6,6,-hexaethyl-l,3,5,2,4,6- trithiatristanninane blended with 90 parts of a complex grease and the composition of Example IX comprising eight parts of 2,2,4,4,6,6-hexamethyl-l,3,5,2,4,6-trithiatristanninane in 92 parts of a complex lithium stearatecalcium stearate hydrocarbon base grease provide superior lubrication as compared with their respective base lubricant compositions when tested in the above manner.

Further tests were conducted in the ER tester in which 8 the four balls were one-half inch in diameter and made of SAE 52-100 steel. The upper ball was rotated at 1750 rpm. and the duration of each run was one minute.

EXAMPLE "XI An additive-free paraflinic white mineral oil having a sulfur content of 0.07 percent, a kinematic viscosity of 17.15 centistokes at 100F. and 3.64 centistokes at 210F. was tested in the ER tester under the above conditions. The test was conducted at room temperature. At a kilogram loading, the average scar diameter on the three stationary balls was 3.0 mm. In a second run using a load of kilograms, the system failed by welding in less than one minute.

EXAMPLE XII A composition comprising 0.1 percent by weight of 2,2,4,4,6,6, hexamethyl-1,3,5,2,4,6, trithiatristanninane with 99.9 percent of the oil of Example XI was run in the EzP. tester under the general conditions set forth above. The test was conducted at room temperature. At a load of 100 kilograms, the average scar diameter was 3.0 mm. In a test at kilograms the system failed in less than one minute.

These results show that my compositions are efiective. at high loads as well as low loads. As shown, the use of my composition enabled effective lubrication at 100 kilograms. In contrast, the additive-free oil failed at this loading in less than one minute.

Similar results are obtained with other of my lubricant compositions. Thus the composition of Example X comprising seven one-hundredths parts of 2,4,6-triethyl- 2,4,6 trimethyl 1,3,5,2,4,G-trithiatristanniuane blended with 99.93 parts of tricresyl phosphate; the composition of Example V comprising two parts of 2,4,6-triethyl-2,4,6- trimethyl-l,3,5,2,4,6-trithiatristanninane blended with 98 parts of bis(methylphenoxy) benzene; and the composition of Example VII comprising three one-hundredths parts of 2,2,4,4,6,6-hexametl1yl-l,3,5,2,4,6-trithiatristanninane blended with 99.97 parts of commercial polybutene oil provide superior lubrication as compared with their respective base compositions when tested in the above manner.

My compositions are multifunctional in that they are not only good lubricants but are also extremely oxidatively stable. In order to demonstrate this oxidative stability, they were tested in the Polyveriform Oxidation Stability Test (see Factors Causing Lubricating Oil Deterioration in Engines, Ind. and Eng. Chem, Anal Ed, 17, 302 (1945)). This test effectively evaluates the performance of lubricating oil antioxidants. The test equipment procedure employed and correlation of the results with engine performance are discussed in the paper cited above.

My test procedure employs a slight modification from that of the publication; it does not use the steel sleeve and copper test piece there described. The conditions used involved passing 48 liters of air per hour through the oil composition for 20 hours. The oil is held at 300 F. during this period. Oxidative deterioration of the oil was promoted by employing oil soluble oxidation catalysts, namely 0.05 percent by weight of ferric oxide as ferric 2-ethylhexoate and 0.10 percent by weight of lead bromide dissolved in the composition being tested. Following the tests the amount of oxidation of the test composition was determined by three factors:

(1) The percentage increase in the viscosity of the test composition as measured at 100 F.

(2) The acid number of the test composition after testing.

' (3) The visual sludge rating. The amount of sludge present after test is determined visually and denoted by a letter varying from A to E. A denotes a very clean composition with little or no sludge whereas B, C, D and E denote increasing amounts of sludge present in the composition.

9 EXAMPLE XIII A Mid-Continent chlorex solvent-extracted propanedewaxed base mineral oil was tested in the Polyveriform Test under the above conditions. The sulfur content of the base oil was 0.17 percent, the flash point (ASTM D 92) was 405 F. and the viscosity at 100 F. was 233 Saybolt Universal seconds. Following the test the acid number was found to be 4.8 and the percent viscosity increase was 106. The visual sludge rating was B.

EXAMPLE XIV A composition comprising one percent by weight of 2,2,4,4,6,6 hexamethyl-l,3 ,S,2,4,6-trithiatristanninane in the base oil of Example XIII was tested in the Polyveriform Test under the same conditions. After testing, the acid number of the composition was 1.7, the percent viscosity increase was nine and the visual sludge rating was A.

The above examples show the extreme oxidative stability of lubricant compositions of my invention. The acid number, the percent viscosity increase and visual sludge rating of my lubricant compositions are vastly improced over the base material.

Other of my compositions show great resistance to oxidation when tested in the Polyveriform Oxidation Stability Test as described above. Thus, the lubricant composition of Example VI comprising four parts of 2,2-diethyl- 6,6-dimethyl-l,3,5,2,4,6-trithiatristanninane in an LB-165 polyalkylene glycol oil; the lubricant composition of Example VIII comprising six parts of 2-ethyl-6-methyl-l,3,5, 2,4,6-trithiatristanninane blended with 94 parts of a tetrahydrofuran-ethylene oxide copolymer oil and the lubricant composition of Example IV comprising five parts of 1,3,5,2,4,6-trithiatristanninane in 95 parts of bis (n-do decyl) di-n-propyl silane are much more resistant to oxidation than are their respective additive-free base materials when tested in the above manner.

In order to further illustrate the oxidative stability of my compositions, they were subjected to the Panel Coker Test. This test is described in the Aeronautical Standards of the Departments of Navy and Air Force, Spec, MIL-L- 7808C, dated November 2, 1955. The Panel Coker ap paratus was operated at 550 F. for 10 hours on a cycling schedule with the splasher being in operation for five seconds followed by a quiescent period of 55 seconds. On completion of these tests, the extent to which the test oil had decomposed was determined by weighing the amount of deposits formed on the metallic panel. The test results are as follows:

EXAMPLE XV An additive-free Mid-Continent chlorex solvent-extracted propane-dewaxed mineral oil as described in Example XIII was tested in the Panel Coker Test under the above conditions. Following the test, the panel was weighed and the amount of deposit formed was determined to be 434 milligrams.

EXAMPLE XVI A mixture comprising 0.5 percent by weight of 2,2,4,4, 6,6 hexamethyl l,3,5,2,4,6-trithiatristanninane and the mineral oil of Example XIII was tested in the Panel Coker under the above conditions. On completion of the test only 12 milligrams of deposit had been formed on the panel.

The results set forth in Examples XV and XVI further demonstrate the great superiority of my lubricant compositions relative to a non-additive base oil in terms of oxidative stability. As shown, the deposit resulting from my composition (Example XVI) was 12 milligrams whereas the deposit from the base oil (Example XV) was 434 milligrams. Thus, in terms of the Panel Coker Test, my composition was approximately 36 times more effective than the non-additive base oil.

All of my lubricant compositions show increased oxidative stability as compared with their respective base fluids when tested in the Panel Coker Test as set forth above. As illustrative examples, the lubricant composition of Example VII comprising three one-hundredths parts of 2,2,4,4,6,6-hexamethyl-l,3,5,2,4,6-trithiatristanninane blended with 99.97 parts of a commercial polybutene oil; the lubricant composition of Example X comprising seven one-hundredths parts of 2,4,6-triethyl-2,4,6- trimethyl 1,3,5,2,4,S-trithiatristanninane blended with 99.93 parts of tricresyl phosphate; and the lubricant composition of Example VI comprising four parts of 2,2-diethyl-6,6-dimethyl-1,3,5,2,4,G-trithiatristanninane blended with an LB-l65 polyalkylene glycol oil, prove superior to their respective base fluids when tested in the Panel Coker Test.

The examples and the data set forth in this specification are by way of illustration only and should not be construed as limiting the scope of my invention. Obvious variations within the scope of the invention will be readily apparent to one skilled in the art. As an example, one can use a plurality of the hereinbefore specified trimeric tin sulfide compounds as additives to a single base lubricant composition. Further, one can use as the base lubricant composition a mixture of a number of synthetic lubricants or a combination of synthetic and natural lubricant materials. As an example, one could use a mixture of a dimethyl siloxane with a mineral base hydrocarbon oil.

My compositions can contain other components such as conventional soaps, antioxidants, thickeners or additives which are present in commercial oils and greases. Such additives in no way inhibit the effectiveness of my compositions. Further, my compositions may be used as lubricants for a wide variety of materials and find application in the lubrication of such diverse materials as tungsten carbide, titanium, glass, polyvinyl chloride, steel, gold, polyethylene, aluminum oxide and nylon.

My compositions have great utility in lubricating electrically conductive noble metal lubricating systems such as for example, silver-silver or silver-graphite contacts found in electrical switches, motors, relays and electrical generating equipment. The lubricant films laid down by my compositions have high electrical conductivity and therefore would not inhibit the transfer of electric current between the lubricated members.

Having set forth and described the invention fully by way of the foregoing examples and explanation, I desire to be limited only by the scope of the following claims.

I claim:

1. A lubricant composition comprising a major proportion of a lubricant base selected from the class consisting of hydrocarbon oils, hydrocarbon greases, silicon containing oils, silicon containing greases, fluorine containing oils, poly ester oils, poly ester greases, poly alkylene glycol oils, poly alkylene glycol greases, tetrahydrofuran polymer oils, tetrahydrofuran polymer greases, hydrocarbon polymer oils, phosphate ester oils and aromatic ether oils, and from about 0.03 percent to about 10 percent by weight of a trimeric tin sulfide compound having the formula in which the R's are selected from the group consisting of methyl, ethyl and hydrogen, as an anti-wear agent.

2. The lubricant composition of claim 1 wherein the trimeric tin sulfide compound is 2,2,4,4,6,6-hexarnethyll,3,5,2,4,6-trithiatristanninane.

3. A lubricant composition comprising a major proportion of a hydrocarbon lubricating oil and from about 1 1 0.03 to about 10 percent by Weight of a trimeric tin sulfide compound having the formula Ra S R4 in which the R groups are selected from the group consisting of methyl, ethyl and hydrogen, as an anti-Wear agent.

4. The lubricant composition of claim 3 wherein the 12 trimeric tin sulfide compound is 2,2,4,4,6,6-hexamethyl- 1,3,5,2,4,6-trithiatristanninane.

References Cited in the file of this patent UNITED STATES PATENTS 2,288,288 Lincoln June 30, 1942 2,789,103 Weinberg et a1 Apr. 16, 1957 2,891,922 Johnson June 23, 1959 OTHER REFERENCES Georgi: Motor Oils and Engine Lubrication, Reinhold Pub. Corp., New York, 1950, pp. 218-254. 

1. A LUBRICANT COMPOSITION COMPRISING A MAJOR PROPORTION OF A LUBRICANT BASE SELECTED FROM THE CLASS CONSISTING OF HYDROCARBON OILS, HYDROCARBON GREASES, SILICON CONTAINING OILS, SILICON CONTAINING GREASES, FLUORINE CONTAINING OILS, POLY ESTER OILS, POLY ESTER GREASES, TETRAHYDROFURAN POLYMER OILS, TETRAHYDROFURAN POLYMER GREASES, HYDROCARBON POLYMER OILS, PHOSPHATE ESTER OILS AND AROMATIC DROCARBON POLYMER OILS, PHOSPHATE ESTER OILS AND AROMATIC ETHER OILS, AND FROM ABOUT 0.03 PERCENT TO ABOUT 10 PERCENT BY WEIGHT OF A TRIMERIC TIN SULFIDE COMPOUND HAVING THE FORMULA 